On-going and proposed research consists of 2 parallel, closely integrated approaches. The first approach deals with the hypothalamic control of water balance and the magnocellular components, mechanisms, allied structures and hormones which subserve this control. Basic to the success of this type of on-going research has been the utilization of a variety of mammalian species that exhibit a broad range of water balance capabilities, coupled with numerous correlative morphologic techniques. The second format of on-going and future proposed research also deals specifically with ultrastructural correlates of neuroendocrine mechanisms, with emphasis directed toward a more thorough understanding of the function and structure of the mammalian median eminence and contributing tuberoinfundibular, ependymal and glial components which may serve to alter adenohypophyseal metabolism. The specific objectives of this second format will be to define precisely the cellular localization of hypothalamic releasing factors, specifically thyrotropin releasing factor (TRF) and luteinizing hormone releasing factor (LRF) and labeled monoamines with respect to the cellular compartment(s) of synthesis, migration, and ultimate storage in the basal hypothalamus. Completed, on-going and future proposed research also deals with questions that bear upon (1) the neuronal, ependymal and glial contribution to the portal bed of the median eminence, (2) factors (structures) which may functionally link the cerebrospinal fluid (CSF) of the third ventricle with the mantle plexus of portal capillaries, and (3) biological mechanisms that alter the cellular dynamics of parvi and magnocellular neurosecretory neurons of the endocrine hypothalamus.